Power transmission belt

ABSTRACT

The invention comprises a multi-ribbed belt having a tensile cord. The tensile cord having areas of opposite twist along a length of a single cord. In particular, a tensile cord comprises S twist sections and Z twist sections. An S twist section is separated from a Z twist section by a node, thereby creating alternate S twist and Z twist sections along a length of a tensile cord. Therefore, the inventive belt comprises a belt having a tensile cord having a random distribution of S twist sections and Z twist sections along a length of the belt as well as across a width of the belt. This significantly reduces tracking force while using only a single cord in belt construction.

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. provisional application serial No. 60/309,276 filed Aug. 1, 2001.

FIELD OF THE INVENTION

[0002] The invention relates to power transmission belts, more particularly to power transmission belts having a tensile cord having both Z twist and an S twist sections.

BACKGROUND OF THE INVENTION

[0003] Power transmission belts generally comprise an elastomeric body and an embedded tensile cord. The tensile cord may comprise a single strand or a yarn. In the case of yarn, the yarn strand may comprise an S twist or a Z twist. The tensile cord in the belt would then comprise either an S twist yarn or a Z twist yarn. The S and Z notation refers to the “handedness” of the yarn and is characterized by the diagonal form of the ply having a diagonal analogous to an “S” or “Z” letter, see FIGS. 8A and 8B.

[0004] In certain belts, the tensile member cord comprises two separate cords, each having opposite twist construction. In particular, a cord having a “Z” twist construction is located adjacent to a cord having an “S” twist construction. The use of adjacent cords having opposite twists is to address the problem caused by tracking force. Tracking force is the force caused by the torque of the cord twist as load is applied to the belt. Tracking force will cause a belt to be noisy and to wear prematurely due to excessive heating. In the prior art tracking force is reduced by having separate cords, each having opposing twist directions, running adjacent to each other through a belt body.

[0005] The cords may be applied by one of two methods. First, a cord having a first twist, say a Z twist, is applied with spacing for the second cord having an opposite or S twist. The second method is to spiral both Z twist and S twist cords on the belt build at the same time using separate spools, creels and application rollers.

[0006] Representative of the yarn art is U.S. Pat. No. 4,402,178 (1995) to Negishi et al. which discloses a multifilament textured yarn having alternating twists thereon.

[0007] Also representative of the yarn art is U.S. Pat. No. 3,434,275 (1969) to Backer et al. which discloses strands having S and Z twists that are joined by bonding, fusing, or entanglement.

[0008] The prior art with respect to belts requires two separate cords having opposing twists to control tracking force. This requires means for handling and applying two cords during belt construction, resulting in decreased efficiency and increased cost.

[0009] What is needed is a power transmission belt having a single tensile cord with discrete alternating Z twist and S twist sections. What is needed is a power transmission belt having a tensile cord with both Z twist and S twist sections randomly distributed along a length of the belt. What is needed is a power transmission belt having a tensile cord with both Z twist and S twist sections randomly distributed across a width of the belt. What is needed is a power transmission belt having a single tensile cord with alternating Z twist and S twist sections that neutralize a tracking force. The present invention meets these needs.

SUMMARY OF THE INVENTION

[0010] A feature of the invention is to provide a power transmission belt having a single tensile cord with discrete alternating Z twist and S twist sections.

[0011] Another feature of the invention is to provide a power transmission belt having a tensile cord with both Z twist and S twist sections randomly distributed along a length of the belt.

[0012] Another feature of the invention is to provide a power transmission belt having a tensile cord with both Z twist and S twist sections randomly distributed across a width of the belt.

[0013] Another feature of the invention is to provide a power transmission belt having a single tensile cord with alternating Z twist and S twist sections.

[0014] Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.

[0015] The invention comprises a multi-ribbed belt having a tensile cord. The tensile cord having areas of alternate twist along a length of a single cord. In particular, an S twist section is separated from a Z twist section by a node, thereby creating alternate S twist and Z twist sections along a length of a tensile cord. As a result, the inventive belt comprises a belt having a tensile cord having a random distribution of S twist sections and Z twist sections along a length of the belt as well as across a width of the belt. This significantly reduces tracking force while using only a single cord in belt construction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a plan view of a tensile cord.

[0017]FIG. 2 is a detail of a node.

[0018]FIG. 3 is a belt cross-section at line 3-3 in FIG. 6.

[0019]FIG. 4 is a belt cross-section at line 4-4 in FIG. 6.

[0020]FIG. 5 is a cross-section view of a prior art belt having separate S twist and Z twist cords.

[0021]FIG. 6. is a perspective view of the inventive belt.

[0022]FIG. 7 is a plan view of an alternate tensile cord.

[0023]FIGS. 8A and 8B are representations of an S twist and a Z twist.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024]FIG. 1 is a plan view of a tensile cord. This form of yarn twist includes separate Z twist and S twist sections in a single tensile cord. Each Z twist section is separated from an S twist section by a node, thereby creating alternate S twist and Z twist sections in a tensile cord. Cord 10 may comprise any tensile cord material known in the art including nylon, polyester, aramid, rayon, PEN, fiberglass and carbon fiber.

[0025] Cord 10 comprises alternate twist plied yarn comprised of alternating sections of S twist and Z twist, such as section 5 and section 6 respectively. The S and Z twist sections are not coextensive, being separated by reversal nodes or bonds 3. The distance between reversal nodes is the twist length measured in turns per inch. A twist length for the Z twist is L1. A twist length for the S twist is L2.

[0026] In FIG. 1, the distance C represents one cycle from a first S twist section to the next S twist section. L1 represents the first partial cycle of Z twist and L2 represents the second partial cycle of S twist.

[0027] Each S twist section and Z twist section may have equal lengths or may be of unequal lengths, each giving a favorable result, i.e.:

L1=L2

or

L1≠L2

[0028]FIG. 2 is a detail of a node. One turn of the S twist section is 11 a. One turn of the Z twist is 11 b. Each strand having an S twist is depicted by 12 and 12 a. Node 3 is formed by the process described in U.S. Pat. No. 5,829,241 and U.S. Pat. No. 4,873,821 among others, incorporated herein by reference. The yarn singles strands are unwound and passed through holes in a baffle board and then through tensioners before entering a torque jet. The yarns are twisted into an S twist or Z twist before exiting the torque jet. They may then ply together into a plied yarn strand that passes through a booster torque jet. The booster torque jet may be used to assist the torque jet in generating singles twist so slightly higher ply twisting is achievable. The yarn is then passed through another torque jet that imparts an opposite twist at each node, thereby creating an alternate S twist and Z twist along a length of a tensile cord. In the preferred embodiment, the plied yarn strand does not pass through a bonder at each node, instead relying solely on the entanglement and overplying caused by the torque jet and booster jet at each node 3. The inventive belt is not limited to using cord produced by the method described herein. Other methods known in the art are available to produce a tensile cord having discrete, alternate S twist and Z twist sections. Each cord having this characteristic will produce a satisfactory result in the inventive belt.

[0029]FIG. 3 is a belt cross-section at line 3-3 in FIG. 6. The inventive belt comprises elastomeric body 100. Elastomeric body 100 may comprise any material known in the power transmission belt art, including EPDM, SBR, CR, HNBR, BR, and NBR. The inventive belt comprises a multi-ribbed profile 101. The belt may also comprise any profile known in the art, including a v-belt or toothed profile. The tensile cord having the alternating S twist 102 and Z twist 103 is embedded in elastomeric body 100.

[0030] During fabrication, the tensile cord is applied to the belt body in a continuous fashion such as in a helical wrap. For example, the cord is wound upon the belt layer(s) on a build mandrel as is known in the art.

[0031] Unlike the prior art, the inventive belt requires only a single tensile cord spool comprising both S twist and Z twist sections as described herein. The prior art requires a separate S twist cord and a separate Z twist cord applied simultaneously to fabricate a low tracking force belt. In the inventive belt, since the S twist sections and Z twist sections are randomly distributed along a length of a single tensile cord, the S twist and Z twist sections are randomly distributed along a length of the belt as well as across a width of the belt. The random distribution of S twist and Z twist sections significantly reduces or neutralizes a belt tracking force without the need for separate S twist and Z twist tensile cords.

[0032] A belt tracking force is caused by the action of a tensile cord when the belt is under a tensile load. The twist of the tensile cord will cause the belt to track, or move to one side of a belt centerline during operation. Tracking can cause excessive noise, heating and wear, leading to premature failure. Reducing or neutralizing the tracking force causes a commensurate reduction in noise and wear caused by the belt tracking properly in a pulley. This, in turn, results in increased belt life by reducing heat and fatigue.

[0033] Further, using a single tensile cord feedstock having alternate twists instead of two separate feedstocks, each having a different twist, simplifies the belt fabrication process thereby reducing the cost of each belt.

[0034] An illustration of the random distribution if S twist and Z twist sections in the belt is shown in FIG. 4, a belt cross-section at line 4-4 in FIG. 6. FIG. 4 represents a cross-section of the belt taken across a location different than that represented in FIG. 3. The S twist sections 102 and Z twist sections 103 have a distribution that differs from the distribution in FIG. 3 because of the random nature of the location of each S twist section and Z twist section in the tensile cord in the belt.

[0035]FIG. 5 is a cross-section view of a prior art belt having separate S twist and Z twist cords. The belt has a multi-ribbed profile 101. S twist cords 102 and Z twist cords 103 are shown in an alternating arrangement where each S twist cord is flanked by Z twist cords, and vice versa.

[0036]FIG. 6 is a perspective view of the inventive belt. S twist sections 102 and Z twist sections 103 are shown embedded in the elastomeric body 100.

[0037]FIG. 7 is a plan view of an alternate tensile cord. A base yarn is twisted into a three strand, each strand having an S twist and having a predetermined number of turns per inch. Each strand having an S twist is individually depicted by 12 and 12 a and 12 b. The three separate S twist yarns are then twisted with a cord having an overall Z twist at a predetermined number of turns per inch. This embodiment results in tensile cord that is homogeneous along a length. Although a certain number of strands are identified in this description for each S twist, the number is exemplary and not offered to limit the number of strands that could comprise a tensile cord. Further each separate strand may comprise a Z twist and the overall cord may have an S twist with the same result in the inventive belt.

[0038]FIGS. 8A and 8B are representations of an S twist and a Z twist.

[0039] Although a single form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein. 

I claim:
 1. A belt comprising: an elastomeric body; a tensile cord embedded in the elastomeric body in an endless direction; and the tensile cord having alternate Z twist sections and S twist sections along a length of the tensile cord.
 2. The belt as in claim 1 further comprising: the S twist section having a length; the Z twist section having a length; and the S twist section length is not coextensive with the Z twist section length.
 3. The belt as in claim 1 wherein: each of the S twist sections and Z twist sections are randomly distributed across a width of the belt.
 4. The belt as in claim 1 further comprising a profile.
 5. The belt as in claim 4, wherein the profile comprises a multi-ribbed profile.
 6. The belt as in claim 1, wherein each S twist section and Z twist section comprise unequal lengths.
 7. The belt as in claim 1, wherein the tensile cord comprises: a Z twist comprised of at least two strands, each of the strands having an S twist. 